The present invention is directed to data base systems and more particularly to a method of performing a backup dump of the contents of a data base system.
In modern day retail merchandising systems, which consist of a primary data terminal device and a plurality of remote secondary terminal devices, data generated by the secondary terminal devices during a merchandising operation is normally transmitted and stored in a disk file located in the primary terminal device. A backup system has been utilized to ensure that no data is lost when the primary terminal device becomes disabled. The backup system includes a second primary terminal device which receives the same data as the first primary terminal device during a merchandising operation. When the second primary terminal device becomes disabled or is withdrawn from operation, the data stored in the first primary terminal device is required to be downloaded to the second primary terminal device at the conclusion of a day's operation so as to update the data in the second primary terminal device. In downloading the data base, all the data space in the disk file is transferred regardless of whether the file contains stored data, hereinafter referred to as valid data, or empty space which contains no data, hereinafter referred to as invalid data. As the memory capacity of the present day terminal devices increases, the time required for downloading the data base of the first primary terminal device has increased to the point that the operation cannot be completed before the start of the next day's activities.
It is therefore a principal object of this invention to provide a method for downloading a disk file which transfers only the valid data stored in the disk file.